The present invention relates generally to traction-type elevator safety systems and, in particular, to an improved elevator safety plank assembly adapted to be attached to an elevator car in a traction-type elevator system.
Elevators and their associated mechanical components are well known. Elevators are used to move people and equipment between floors or levels in multistory buildings or mines. A conventional traction type elevator application includes an elevator car mounted in a car frame attached to a counterweight via a steel wire rope or cable. A machine positioned at the top of a hoistway drives a traction sheave that is engaged with the rope such that the car and the counterweight are suspended. As the machine turns the sheave, friction forces between the grooved surface of the sheave and the rope move the rope and thereby cause the car frame and counterweight to raise and lower in opposite directions in the hoistway. The hoistway typically has a set of at least two vertical beams or rails on which the elevator car moves. The elevator car is coupled to the rails by guide shoes that typically include emergency brakes. The rails absorb side to side loads during operation of the elevator. These side loads, as well as vibration forces from the machine, suspension cable, and brakes are isolated from the interior of the car by various isolation means, including rubber dampers and the like.
Traction-type elevators also often include compensation cables, which cables attach at opposite ends of the bottoms of the elevator car and the counterweight and are operable to compensate for imbalances caused by the weight of the suspension cable when the elevator car and the counterweight are vertically spaced apart. In addition, a traveling or trail cable, which provides electrical power to the elevator car, is connected to the elevator car and travels with the car through the various floors. A device known in the art as a safety plank is attached to the bottom of the elevator car and includes a mounting means for the compensation cable sheaves.
Following the installation of an elevator assembly, the elevator car must be balanced within the hoistway for optimum operation. This requirement to balance the car is inherent in traction-type elevators, because of the imbalance caused by the suspension ropes, the trail cables, the compensation cables as well as the design of the cars within the allowed hoistway space. Prior art balancing practices include the application of a weight frame, adjusting the position of the car frame within the hoistway to achieve balance, and positioning equipment, such as the suspension cable and compensation cable, at predetermined locations in order to balance the car properly. The balancing of the car provides for guide shoes and rail loads within the specified requirements of the shoes and rails. Normally the goal is to achieve a zero load on the guide shoes with the car balanced at the middle of the hoistway. Balancing the elevator car during installations of prior art elevator systems, however, was made more difficult because the elevator systems utilized different components for the component interfacing, assembly, adjustment, and balancing causing each elevator system to be different.
It is desirable, therefore, to provide an assembly operable to include multiple attachments that will allow for balancing of the elevator car on site. It is also desirable to provide an assembly that will combine component interfacing, assembly, adjustment, and balancing into a unitary assembly.
The safety plank assembly according to the present invention is used with a traction-type elevator having a drive machine at the top of a hoistway in a machine room or mounted at the top of a rail. The assembly includes two spaced apart safety plank beams of C-shape profile extending parallel to one another. When the assembly is mounted on the bottom of an elevator car, the plank beams extend the width of the car from rail to rail. The plank beams are spaced apart by a greater distance than prior art safety plank beams, thus providing better support for the platform and improved isolation means. The plank beams are connected by a cross support member and one or more of end plates, bottom plates and transverse members. A rope sheave is rotatably mounted on each opposed end of the safety plank assembly. Each sheave is oriented to define a diagonal rope path through the assembly for underslung support of the elevator car. A plurality of balancing weights and traction weights can be mounted on the assembly. Safety mounting provisions are included in the assembly for attaching safety equipment such as emergency brakes.
The elevator suspension ropes are routed around the sheaves and between the safety plank beams through apertures in end plates or gaps in end walls of the assembly. Thus, the suspension ropes and the bottom pinch points associated with the sheaves and rope movement are housed within the safety plank assembly, which provides a degree of safety for personnel working under the car. In one embodiment of the safety plank assembly, the sheaves are mounted on two sheave beams attached to the cross support member. The traction weights are installed between the sheave beams on transverse spacer members, and the balancing weights are installed in weight brackets on the main plank beams. In another embodiment of the safety plank assembly, the sheaves are mounted on angled gussets fastened to the bottom plates. The traction weights and balancing weights are installed on transverse members extending between the main plank beams and the cross support member.
The safety plank assembly according to the present invention advantageously includes all component interfacing, assembly, adjustment and balancing in a unitary assembly. The safety plank assembly according to the present invention is designed for installation of the necessary weight required to meet the traction requirements of the machine and ropes. The traction weights can be added either in the factory or at the installation site, before or after the car is installed. The additional weight is added to the safety plank assembly by inserting the necessary amount of cut weight plates at specific locations on the safety plank assembly to balance the car within the hoistway. The safety plank assembly also contemplates the addition of weight to counterbalance the weight of compensation or traveling cables by locating weight plates at other specific locations. The attachment of the compensation cables is accomplished by the use of one weight or a bracket designed for this attachment and located in the safety plank at the necessary location.